One drawback to longwall mining is the time consumed in moving the face equipment from one panel to the next. The average move time in U.S. longwall operations is 20 days, while moves taking as long as 30 days are not unusual. Bethenergy Mines Inc., working with the Bureau of Mines, looked for ways to speed up this phase of longwall operations for its mine No. 60 In southwestern Pennsylvania. Engineers from Bethenergy and the Bureau found that by using predriven longwall recovery rooms and specially constructed roof- supporting piers, which are subsequently mined by the longwall, the mine is able to complete panel extraction by an average of 12.5 Days faster and reduce face-equipment move time by 30 pct. In addition, longwall production is maintained right to the end of the panel. Although the predriven room recovery technique increased support costs by two to four times over those of conventional methods, the use of such recovery rooms boosted the mine's productivity.
Coal, V. 26, No. 3, Mar. 1989, PP. 69-70